The present invention relates to alloys of iridium and silicon, as well as to alloys of ruthenium and silicon, and to structures bearing coatings of such alloys. More particularly, the present invention relates to compositions of iridium and/or ruthenium, and silicon which resist oxidation at elevated temperatures and to structures suitable for use at higher temperatures which are, at least in part, protected from oxidation by having surface coatings of alloys of iridium and/or ruthenium, and silicon.
It is known that there are many alloys which have desirable sets of properties, particularly combinations of properties which render them suitable for use as structural elements. However, the use of alloys at higher temperatures results not only in the change in the properties which the alloy exhibits but also results in a tendency toward oxidation of the alloy at its surface. If the oxidation is of a character which continues then the structural element itself can fail because of the conversion of the metal of the structure to oxide or other product resulting from oxidation. Most irons and steels are notorious for the oxide or rust coating which forms on the surface thereof and extensive coating or painting is required to preserve the surface free of rust.
Other alloys or alloy systems also are highly subject to oxidation and oxidation rates have been measured by heating a sample of an alloy over a period of time and measuring the weight gain of the sample, as an adhesive oxide is formed at the surface, or a weight loss occurs because of a scaling of oxide at the surface together with a flaking of the oxide scale from the surface. Novel and unique properties are possible in a number of structural elements if the elements could be protected from the results of oxidation or other oxidative reaction. For example, carbon fiber composites have uniquely high strength and other valuable properties but such structures are subject to oxidation to form gaseous carbon monoxide or carbon dioxide. A great variety of proposals have been made for protecting structural elements including carbon fiber composites from oxidation for various periods of time during which the structure can be employed in carrying out its intended function.